You can't resurrect Astarion. I killed him in the bite scene too, then was annoyed by his corpse and tried resurrecting him with Withers and with a scroll - nothing works. And the companions talk about him, as If he were alive.
And nearly as annoying: when you try to send him away, He just stays. Astarion just doesn't know, when to leave.
As for opening locks and disarming traps: Shadowheart is a really good substitute. With the trickery domain she has some nice feats, that help her stay hidden and her sleight of hand is great - especially combined with Guidance. Trust me, I don't bother with Astarion anymore ( I just kill him in the first meeting) since a few playthroughs and it works great.
